Why are we still looking for extraterrestrial intelligent life?

A6021 should we lower the standard when searching for extraterrestrial life?

Sina science and technology news Beijing time on November 17, mankind has been searching for signs of the existence of other advanced civilizations in the universe, but so far nothing has been found. From this point of view, perhaps we should not only focus on intelligent life, any type of life form is worth looking for. Of course, small microbes may not be as exciting as aliens, but in the Milky way, signs of non intelligent life may be much more common and easier to find than intelligent life.


Life has successfully evolved on earth, including intelligent life. But the earth should be nothing special, just an ordinary planet in the Milky way. Therefore, since intelligent life can appear on earth, it should also be very common in the Milky way, and the traces of alien civilization should be seen everywhere.

The question is, where have they all gone?

This is the core argument of the famous Fermi paradox and the cornerstone of the SETI (search for extraterrestrial intelligent civilization) project. At first glance, it seems that human beings cannot be the only existence in the universe. If we look carefully enough, we should be able to find evidence of the existence of intelligent life.

Maybe aliens will deliberately send radio signals to us; Maybe they will send signals in all directions, and we just happen to receive them; Maybe they left some scientific and technological products in the solar system to monitor us; Maybe they will carry out large-scale engineering projects, such as wrapping the whole star with solar panels; Or they will fly around and pollute their stars with heavy metals, so as to announce their existence to the outside world.

However, after more than half a century of SETI project, we still have nothing. No radio signal was found; No scientific and technological products were found; No major projects were found. So far, we have carried out more than 100 special searches, but we have not found any evidence of intelligent life in the Milky way or even in the whole universe.

Traces of life

SETI project believes that intelligent life should be easier to find than ordinary non intelligent life, because intelligent creatures will leave many signs and announce their existence to others. If they have invented radio technology, they can spread the message of their existence at the speed of light through “frequency modulation”. If they can harness a considerable part of the stellar energy, they can transform the whole planetary system. If they have conquered Star Trek, they can spread the “seeds” of their wisdom all over the universe.

But there is clearly something wrong with this assertion. Intelligent life is either not as common as we think, or it is not as easy to detect as we hope. In either case, the SETI project does not seem to achieve any results in a short time.

Therefore, we should probably focus on “extrasolar life” rather than “advanced alien civilization”. The former means any type of life, such as single celled organisms floating in the ocean, moss attached to stones, or complex life that can move freely in the environment.

These life forms may not be as conspicuous as aliens, but it doesn’t mean they can’t be found at all. After all, one of the most critical features of life is the ability to break the planetary equilibrium.

Take the earth’s atmosphere as an example. When the earth was first formed, the content of oxygen may be very high, because there was no lack of oxygen in the universe. However, oxygen is highly volatile and active. It cannot remain in the atmosphere for too long. It will either escape into space or combine with various elements and become other substances (such as carbon dioxide or silicon dioxide). But about 2 billion years ago, the number of single celled microorganisms capable of photosynthesis increased sharply, swallowed a lot of carbon dioxide, and then released a lot of oxygen, which completely changed the state of the earth’s atmosphere.

When a distant exoplanet passes in front of its own star, the light emitted by the star will pass through the planet’s atmosphere. Different elements and molecules in the atmosphere will slightly change the color of these lights. Although the change range is very small, it can be detected.

First contact

Due to the limitation of current technology, it is difficult to analyze the atmosphere of giant planets near other stars. However, NASA’s transit exoplanet survey satellite has listed some potential “candidates” for follow-up after the James Webb telescope takes off. The telescope has the ability to detect excess oxygen in the atmosphere of exoplanets.

Such “first contact” may not be too exciting. We will not exchange indices or basic constants with alien life as in the film, nor will we be curious about alien culture, habits or bodies.

The alien life form we first discovered is most likely some kind of microorganism that will only twist in place. By breaking the equilibrium state of the planet, we can find their existence. Non intelligent life may not be as common as intelligent life (but to be honest, we don’t know how common these two kinds of life are respectively), but simple life forms also have the ability to let others find themselves.

This scene may not be as exciting as launching a space war with aliens, but no matter what kind of alien life is found, it is always an exciting thing. (leaves)